1. Field of the Invention
The present invention relates to a device for contactless measurement of rotor temperatures and including a magnet provided on the rotor and an electrical coil arranged on a stator with which the rotor cooperates, and electronic means for measuring a voltage signal applied to the coil.
2. Description of the Prior Art
The measurement of temperatures of moving objects is a very common problem encountered in technology. When the objects are rotors rotating at very high speeds, only contactless measurement methods are considered. Additional boundary conditions further limit the applicability of known measuring methods. One such boundary condition can be operation under vacuum, for example. High-speed rotating mechanical vacuum pumps (e.g., turbomolecular pumps) and centrifuges can be taken as representative for many applications. The importance of temperature measurement and monitoring becomes particularly clear when considering the example of turbomolecular pumps in which specific rotor temperatures may not be exceeded for safe operation of the rotor. An exact and reproducible temperature monitoring is indispensable for this purpose.
In many areas of technology, pyrometers are used for contactless temperature measurement. These pyrometers measure the radiation coming from the rotor as a measure of its temperature. An example for an arrangement of this kind is shown in EP 1 348 940 A2. The radiation sensed by sensors depends not only on the temperature but also to a great extent on the surface condition of the rotor. Temperature measurements may be corrupted when pumping vaporous media particularly in processing technology, in that the surface of a pump rotor is subject to changes caused by condensation, deposit of solid particles, or chemical reactions. Further, expensive compensating electronics are required because of the dependency of the readings on the ambient temperature and housing temperature. The sometimes high sensitivity to high-energy ionized radiation limits the range of uses.
DE-OS 43 09 018 describes an arrangement for contactless measurement of rotor temperatures which uses ferromagnetic materials. These ferromagnetic materials are attached to the rotor of the arrangement and, along with additional components at the stator, form a magnetic circuit. Its characteristics change suddenly when the Curie temperature of the ferromagnet is exceeded. With this arrangement, it is only possible to determine that the Curie temperature has been exceeded. Several temperatures can be determined only by using several ferromagnets with different Curie temperatures. The difficulty arising in the use of an arrangement of this kind on a larger scale consists in procuring ferromagnetic materials with a reproducible Curie temperature. Further, it is possible to take measurements over necessary temperature ranges only by devoting considerable resources with the resulting high costs.